G.hn is the latest ITU-T home network standard, which provides a networking technology within the home user network based on power lines, telephone lines, coaxial lines. The G.hn defines four power modes in total. Transceiver should work in one of the following modes during the boot-up:                Full power mode (L0): in this mode, data transmission can reach the maximum rate. Power consumption is only limited by the power spectral density (PSD).        High-efficiency Mode (L1): in this mode, power consumption is reduced by limiting the media access to part of the MAC (Medium/Media Access Control) cycle. The maximum data rate is supported.        Low-power mode (L2): in this mode, power consumption is reduced by compressing the media access in a plurality of MAC cycles, and only a limited data rate is supported.        Idle mode (L3): in this mode, the power consumption is minimized by compressing the media access in a long period of MAC cycle. The transceiver is booted up and physically connected to the home network, but no data other than control messages are sent or received.        
In this text, the power modes are divided into non-energy-saving mode and energy-saving mode, in which the full-power mode (L0) is the non-energy-saving mode, and the high-efficiency mode (L1), the low-power mode (L2) and the idle mode (L3) are collectively called the energy-saving mode.
The G.hn defines the concept of logical network “domain”, and the domain is identified with a domain name (referred to as DN), in general, different homes use different domain names, which is similar to the SSID (Service Set Identifier) of WiFi. Each domain has one domain master node (Domain Master) and at least one ordinary node. The domain master node is in charge of management tasks such as access, exit, authentication, and broadband distribution of other intra-domain ordinary nodes. The other nodes can send messages to the domain master node and request to be in idle in multiple MAC cycles.
A node in the idle state does not perform any interactions, so that the domain master node should not allocate any dedicated resources (such as contention-free time slot (CFTS) or contention-free transmission opportunity (CFTXOP) to this node. However, the node in the idle state can still transmit within the TXOP (Transmission Opportunity) or time slot in which the MAP allows it to transmit. If the transmission of the node in the idle state requests to be acknowledged, the node should be prepared to receive an ACK frame from a target node. The target node can send an acknowledgment to the node in the idle state. Except this case, other nodes cannot send messages to the node in the idle state.
A node can request for two kinds of long-term idle scheduling: if the node expects that the scheduling only takes effect once, it needs to specify the length of the requested idle period. If the node expects that the scheduling takes effect for many times, it needs to specify the length of the requested idle period and the length of the subsequent active period. In this case, the idle period and the subsequent active period will repeat until the domain master node is canceled or changed. If the domain master node accepts the request, it shall inform the node of the recommended idle scheduling. For the long-term idle scheduling, the starting time and length of the idle period and the length of the subsequent active period (if available) should be identified in the auxiliary information field of the MAP message. During the active period, the node can send other idle scheduling to change the current idle scheduling, or send a message to cancel the current idle scheduling. The domain master node can send different idle scheduling at any time to terminate or change the current idle scheduling.
A node can also request for a short-term idle scheduling, and can be in the idle state and the active state within time segments of one MAC cycle respectively.
In the conventional energy-saving mode, there is no specific description about how the domain master node saves energy. At the same time, the start times and the sleeping lengths of ordinary nodes may not be the same, and the energy-saving may request to change or cancel the sleeping plan at any time, therefore the domain master node is hard to save energy during the sleeping.